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Oxygen
Oxygen was a chemical element with symbol O and atomic number 8. It was a member of the chalcogen group on the periodic table and was a highly reactive nonmetallic element and oxidizing agent that readily formed compounds (Notably oxides) with most elements. By mass, oxygen was the third-most abundant element in the universe after hydrogen and helium. At STP, two atoms of the element bind to form dioxygen, a diatomic gas that was colorless, odorless and tasteless with the formula O 2. Oxygen was what we breathed on Earth and was an important part of Gravity. Description Many major classes of organic molecules in living organisms such as proteins, nucleic acids, carbohydrates and fats contained oxygen as the major inorganic compounds that are constituents of animal shells, teeth and bone did. Most of the mass of living organisms was oxygen as it was a part of water, the major constituent of lifeforms (For example, about two-thirds of human body mass). Elemental oxygen was produced by cyanobacteria, algae and plants and was used in cellular respiration for all complex life. Oxygen was toxic to obligately anaerobic organisms which are the dominant form of early life on Earth until O 2 began to accumulate in the atmosphere. Free elemental O 2 only began to accumulate in the atmosphere about 2.5 billion years ago (See Great oxygenation event), about a billion years after the first appearance of these organisms. Diatomic oxygen gas constituted 20.8% of the volume of air. Oxygen was the most abundant element by mass in the Earth's crust as part of oxide compounds such as silicon dioxide, making up almost half of the crust's mass. Oxygen was an important part of the atmosphere and was necessary to sustain most terrestrial life as it was used in respiration. However, it was too chemically reactive to remain a free element in Earth's atmosphere without being continuously replenished by the photosynthetic action of living organisms which used the energy of sunlight to produce elemental oxygen from water. Another form (Allotrope) of oxygen, ozone (O 3), strongly absorbed UVB radiation and consequently the high-altitude ozone layer helped protect the biosphere from ultraviolet radiation, but was a pollutant near the surface where it was a by-product of smog. At even higher low Earth orbit altitudes, atomic oxygen was a significant presence and a cause of erosion for spacecraft. Oxygen was produced industrially by fractional distillation of liquefied air, use of zeolites with pressure-cycling to concentrate oxygen from air, electrolysis of water and other means. Uses of elemental oxygen included the production of steel, plastics and textiles, brazing, welding and cutting of steels and other metals, rocket propellant, oxygen therapy and life support systems in aircraft, submarines, spaceflight and diving. Liquid oxygen was blue. Oxygen was discovered independently by Carl Wilhelm Scheele in Uppsala in 1773 or earlier and Joseph Priestley in Wiltshire in 1774, but Priestley was often given priority because his work was published first. The name oxygen was coined in 1777 by Antoine Lavoisier whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. It's name derived from the Greek roots ὀξύς oxys, "acid", literally "sharp", referring to the sour taste of acids and -γενής -genes, "producer", literally "begetter", because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition. See Also *Hypoxia Category:Science Category:Gravity Category:Trivia